Air heater



wl-r/vs'ss 5r .TTORNL'Y March 2, 1937. J. H. ROHRER 2,072,456

AIR HEATER Filed Sept. 24, 1954 3 Sheets-Sheet l J. H. ROHRER AIR HEATER March 2,1937. 2,072,466

Filed Sept. 24, 1954 3 Sheets-Sheet 2 jeflimlll I I" II lNVE/VTOR mus) Patented Mar. 2, 1937 UNITED STATES PATENT OFFICE Claims.

My invention relates to air heaters by the operation of which the hot gases of combustion, delivered from a boiler and about to be delivered into the stack, are caused to pass through one 5 or more banks of tubes over which a current of air is impelled in a direction counter to that of said gases, whereby the heat of the gases is transferred to said air which in turn may be delivered to the combustion chamber of the boiler, or to any other apparatus for which heated air may be required.

It is an object of the present invention to construct a sectional heater, which heater may be made up of a number of unit sections in accordance with the capacity desired.

A further object of this invention is to provide heat interchange units, each composed of a bank of tubes mounted in header plates and housed in a substantially integral casing, some of the walls of which will form the walls of the finished heater when two or more units are assembled.

A further object of this invention is to provide a construction in which the tubes through which the heated gases pass are straight, are much shorter than those usually employed in ordinary constructions; are of much smaller diameter than those heretofore used; and are set much closer together, thereby to provide for the passage through the tubes of relatively small columns or streams of hot gases and to provide for the passage over and between the tubes of relatively thin streams of air whereby is effected a very rapid transfer of heat from the gases to the air.

A further object of this invention is to substantially reduce the outside dimensions of air heaters and the length of tube therefore required, to obtain a predetermined drop in the temperature of the gases and a predetermined rise in the temperature of the air, by substantially reducing the size of the passage through which the gases flow and by using more pipes or tubes set more closely together, but without interfering with the free rapid passage of the gases through the tube and of the air over and between the tubes.

A further object of this invention is to provide an air heater in which the air and gas will pass at a high rate of speed through and over the tubes, whereby the same will be substantially self-cleaning.

Further objects of this invention will appear in the specification and claims below.

Referring now to the drawings, in which the same reference characters are used throughout the various views to designate the same parts,

Fig. 1 is a side elevational view of an assembled 4-unit heater with parts of the casing broken away to show the interior construction.

Fig. 2 is an end elevational view of the same with parts of the casing and partitions broken away to show the interior construction.

Fig. 3 is a horizontal cross-sectional view, on the line 3-3 of Fig. 1, of the l-unit heater, shown in Figs. 1 and 2.

Fig. 4 is a horizontal cross-sectional view of a 3-unit heater, on a line, such as the line 4-4 of Fig. 1.

Fig. 5 is a cross-sectional view of a 2-unit heater on a line such as the line 5-5 of Fig. 1; and

Fig. 6 is an enlarged horizontal sectional fragmentary view, on the line 4-4 of Fig. 1, showing the close arrangement of the small tubes used in my improved heater.

The completed air heater shown in the drawings, embodies in its construction, a plurality of relatively small heat exchange or interchange units of substantially the same capacity and of substantially the same dimensions.

The assembled air heater shown in Figs. 1 to 4, consists of two similar, but complemental end units A and A (right and left hand, respectively, as shown in Fig. 1) and one or more intermediate heat-interchanging units B. Each end unit (A or A) comprises preferably a rectangular bank I of like parallel tubes 2 having their opposite ends passing through and rigidly secured (preferably by welding) to a top tube-plate 3 and a bottom tube-plate 4 respectively. These tubes 2 are of relatively small diameter and they are closely arranged in a staggered relationship to leave relatively small spaces between them as is plainly indicated in Fig. 6. These tubes are preferably, in internal diameter, only about one-half that of the tubes ordinarily used in air heaters for the heating of air for the combustion chamber of a boiler, and, therefore, in a given area of the top or bottom tube-plate I can readily assemble substantially four times as many tubes as are found in the former type of air heater.

The tubes 2 of each end heat transference unit are surrounded on all sides by four walls, to wit, a pair of walls comprising a front wall 5 and a back wall 6, an outside end wall I and an inset inside wall 8.

One of said pairs of walls (5 or 6) may completely close the space between the top tube-plate 3 and the bottom tube-plate 4 as shown in the drawings, but the invention is not to be construed as limited to the complete closure of a side by either of said walls 5 or 6 as will be made plain below.

The upper edge 9 of the front wall 5 is spaced well below the plane of the top tube-plate to provide an opening extending the full width of the front wall and afford free access to the spaces between the tubes Lof the banks of tubes.

The lower edge I of the said front wall is spaced well above the plane of the bottom tubeplate 4 to afford a similar opening for the full width of the wall to the spaces between the said tubes of the banks I of tubes 2 therein.

The outside end wall I is preferably continuous and completely closes for its full depth the space between the upper top tube-plate 3 and the bottom tube-plate 4. The inset inside wall 8 of the end units A or A is offset inwardly from the plane of the adjacent inner edges of the top tube-plate 3 and bottom tube-plate 4 and fits between the front and back walls 5 and 6 respectively as is clearly shown in Figs. 4 and 5. Its upper edge I I is substantially in the horizontal plane of the upper edge 9 of the wall 5 and its lower edge I2 is substantially in the horizontal plane of the edge III of the wall 5. It therefore leaves uncovered the upper and lower ends of the tubes therein.

When, therefore, an air heater of the smallest capacity required in an air heater of this type is to be constructed, it is only necessary to take the two complemental end units A and A, aline them to bring their corresponding edges into substantial abutment, and weld the same together electrically at the seam lines I3 between the two unit constructions, as indicated in Fig. 5. This leaves a space or chamber I4 between the upper ends of adjacent banks. This space constitutes a lane between adjacent tube banks which permits air freely to enter or leave the tube banks.

But air heaters are generally much larger than a 2-unit construction, and, therefore, I provide the intermediate heat interchanging units B, shown assembled with the end units A and A in Figs. 1 to 4. These intermediatev heat interchanging units comprise each a bank I of tubes 2, a top tube-plate 3, a bottom tube-plate 4 and a front and back wall 5 and 6, all respectively like the corresponding walls of the end units A and A. Each intermediate unit C is, however, provided with two side walls like each other and like the inset inside wall 8 of the end units. In other words, the intermediate unit has two parallel opposite inset end walls 8.

To make a 3-unit construction, such as is shown in Fig. 4, an intermediate heat interchanging unit B is placed between two end units A and A and the adjacent corresponding edges of the top and bottom tube-plates, 3 and 4, and front and back walls 5 and 6 are welded together to make gas tight joints at the seam lines I3 indicated on the drawings.

For a larger air heater two or more intermediate heat interchange units B may be welded together in the same Way along their edges, indicated by the seam lines I3 and then the ends of the assembled intermediate sections are closed in the manner above described by welding thereto the right and left-hand end units A and A respectively as shown in Figs. 1 to 4.

When the units have thus been assembled into a substantially integral, inseparable air-tight and gas-tight air heater, of the capacity required, the entire assembly will comprise a plurality of banks I of straight gas tubes 2, substantially vertically disposed, and rigidly secured to a continuous integral rectangular top tubeplate 3, composed of the unit top tube-plates 3 Welded together, a continuous integral bottom tube-plate 4, consisting of the unit bottom plates 4 welded together, a pair of walls comprising the front wall 5 (composed of the unit front walls 5 welded together) and the back wall 6 also composed of the united unit plates 4 and two opposite outside end walls I, the latter closing the opposite ends of the assembled banks from the top tube-plate 3 to the bottom tube-plate 4. One wall of the pair of walls 5 or 6 will be provided with an opening I5 extending the full width of the heater, and provided with a flange I 6 around it, and communicating with the space within the heater walls, which space includes portions immediately beneath the top tube-plate 3, between the tubes 2 of all of the banks of tubes and the space or chamber I4 between the adjacent banks I of tubes. An air duct II isattached to said flanged opening I 5 and through which cold air is delivered to the heater. One of said pair of walls 5 or 6 is also provided with a similar opening I8 surrounded by a flange I9, to which is attached the duct 29 through which the heated air is conveyed away from the heater, extending the full width of the heater and located immediately above the plane of the bottom tube-plate 4 and communicating with the interior of the heater, which interior includes the spaces between the tubes 2 of each bank of tubes and the space I4 between adjacent banks of tubes.

But to direct the air which enters the heater through the upper opening I5 into the narrow spaces between the individual tubes of the banks of tubes and to cause the air to flow down over the outsides of the tubes 2 in thin layers or streams, and equally throughout the cross-sectional area of the chamber in which are the tubes, the space I2 between the banks of tubes. at or about the level of the lower edge of the opening I5 is preferably closed by a narrow plate 2| welded to the top upper edge I! of adjacent inset inside walls 8, and to the inside of the front and back walls 5 and 6 respectively. A similar plate 22 may likewise be welded to the lower edges I2 of the adjacent walls 8, but it may be omitted if desired, without particularly affecting the emciency of the apparatus. These spaces then b tween adjacent banks I of tubes and between the plates 3 and 2| are chambers through which the air from the duct I'I entering the heater is distributed quickly and evenly throughout the relatively narrow spaces between the tubes, the air entering the end banks in units A and A on two sides, the front from the duct ll and the inner side from the chamber I4, while the air enters the intermediate units B from the front by the duct IT and from the chambers It on both sides of the intermediate units. This insures that the air to be heated shall be intimately and evenly distributed throughout the upper ends of each bank of tubes so that substantially all the tubes are operative to heat the air passing thereover and a substantially uniform temperature is attained and maintained throughout the banks at any selected level. The air does not have to force itself through the closely packed tubes from the front only, but these chambers M, free from obstructions, are operative to discharge the air to be heated, laterally, throughout the tubes of the adjacent bank or banks.

To complete the heater, after the units have been assembled in the manner above described, it I is merely necessary to provide the bottom plate 4 of the assembled heat interchange units with a box-like structure 23 and to weld it to the flanges 24 on the bottom of the bottom tube-plate ii. The said box 23 is provided with an opening 25 on one side and flanges 26 around said opening for the attachment to a suitable conduit 21 by means of which the hot gases are conducted to the heater to be discharged from said box 23 into the tubes 2.

A similar box-like structure 28 is similarly mounted on the top of the top tube-plate 3 and is welded to the flanges 29 thereon. One of its vertical walls is provided with a large opening 3! and flanges 32 for the attachment thereto of a conduit 33 leading to the stack or chimney.

The assembled air heater may be supported in any suitable manner, as, for instance, on beams 3d upon which the projecting outer edges of the bottom tube-plate t rest and by which the whole structure is supported.

By greatly reducing the internal diameters of the tubes through which pass the hot gases and by arranging the tubes closely together in a staggered relationship, the cross-sectional area of the columns of gas passing through the tubes will be relatively small and the streams of air passing over the outsides of the tubes will be very thin, with the result that the heat transference will be rapid and the length of the tubing which must be traversed will be proportionally decreased whereby the actual size of the heater will be very much smaller than those heretofore used and having the same capacity.

Further, the speed at which the gases are required to travel through the smaller diameter tubes is higher than in the old construction, and, although the friction between the hot gases and the tubes and between the air and the outside of the tubes is a little greater than in the old form of construction, I find that these factors tend to scour the tubes, particularly the insides of them, and prevent an accumulation of soot and dust therein. It should be noted that, by reason of the high velocity of flow and the small diameter of the tubes, these tubes are to a great extent self scouring. Moreover, it is a simple proposition, when it is necessary, to clean the tubes by passing a flexible cleaning rod therethrough and that without removing the upper or lower boxes 23 or 28, thereby permitting me to weld the abutting edges of the walls and of the units inseparably together with an air-tight joint, thereby preventing the escape of noxious gases from the heater to the surrounding atmosphere and insuring against the leakage of the air being heated.

The large openings 25 and 3t provide easy access to the interiors of the tubes 2 if the ducts 2i and 33 are disconnected and the large openings l5 and i8 similarly give ready access to the exterior surfaces of the tubes when the ducts ii and is are disconnected and since the tubes are straight and short, they can be mechanically cleaned if necessary.

Having thus described my invention, what I claim and desire to protect by Letters Patent of the United States is:

1. An end unit for a multiple unit air heater, consisting of the combination with a substantially rectangular bank of straight parallel tubes of relatively small diameter closely arranged in a staggered relationship but spaced from each other, of a top tube-plate and a bottom tube-plate through which the ends of said tubes respectively pass and into which they are tightly fitted with a casing for said bank of tubes surrounding the same on the four sides thereof by four walls, including a pair of walls on opposite sides of said bank and comprising a front and back wall, one of said pairs of walls having an upper air inlet opening to the space between said tubes immediately below said top tube plate and extending substantially the full width of the unit and one of said pair of walls being provided with a lower air outlet opening communicating with the spaces between the tubes immediately above the bottom tube plate and extending for substantially the full width of the unit, an outside end wall and an inside end wall on opposite sides of said bank and between said pair of walls, the outside end wall of said unit completely closing the spaces bounded by the upper and lower tube plates and the front and back walls of said unit, and the inner end wall of said end unit being oiiset inwardly from the plane of the adjacent vertical side edges of the front and back walls of the unit and tightly closing for its full length the space between the front and back walls, the upper and lower edges of said offset end walls being spaced respectively from the adjacent surfaces of said top and bottom tube-plates to give access to the spaces between said tubes at both ends thereof.

2. An intermediate unit for a multiple unit air heater, comprising in combination a substantially rectangular bank of straight parallel tubes of relatively small diameter closely arranged in a staggered relationship but spaced from each other, a top tube-plate and a bottom tube-plate through which the ends respectively of said tubes pass and into which they are tightly fitted and a casing for said bank of tubes surrounding said bank on the four sides thereof by four walls, including a pair of walls comprising front and back walls, one of said pair of walls having an upper air inlet opening to the spaces between said tubes immediately below the top tube-plate and extending substantially the full width of the unit, and one of said pair of walls being provided with a lower air outlet opening communicating with the spaces between the tubes immediately above the bottom tube-plate and extending for substantially the full width of the unit, and a pair of inwardly inset parallel end walls on opposite sides of said bank of tubes and extending between the front and back plates, the upper edges of said offset walls being spaced from said top tube-plate and the lower edges of said end walls being spaced from said bottom tube-plate respectively to provide air inlet passages for the entry of air to the spaces between said tubes at the upper ends there of and for an air outlet opening communicating With the spaces between the tubes adjacent the bottom end of said tubes.

3. An air heater comprising in combination a plurality of assembled heat transference units connected side by side to form a unitary structure, said structure including two simiiar complemental end units; each of said end units including a substantially rectangular bank of straight parallel tubes of relatively small diameter closely arranged in a staggered relationship but spaced from each other, a top tube plate and a bottom tube plate to which the ends respectively of said tubes are connected, and a casing for each bank of tubes surrounding said bank on the four sides thereof by four walls, said walls including a pair of end walls on opposite sides of each bank of tubes of a unit and a pair of walls constituting front and back walls, one of said pair of walls having an upper air inlet opening to the space between said tubes immediately below the top tube plate and extending substantially the full width of said unit, and one of said pair of walls being provided with a lower air outlet opening communicating with the spaces between the tubes immediately above the bottom tube plate and extending for substantially the full width of said unit, one of the end walls of each end unit completely closing the spaces between the upper and lower tube plate and extending between the front and back walls of each unit, and the inner end walls of each end unit being offset inwardly from the plane of the adjacent vertical side edges of the front and back walls of its unit and tightly closing for its full length the space between said front and back walls; a hot gas box secured to the lower surface of said bottom tube plate for delivery of hot gases directly into the lower ends of the tubes of all said banks of tubes, a similar box secured to the upper surface of the top tube plate into which the hot gases, after traveling through said tubes, are collected for discharge; means to close the space between the upper ends of the offset walls of adjacent units to form a chamber between said means and said top tube plate, from which chamber incoming air is quickly and substantially uniformly distributed throughout the space between the tubes at the upper ends of adjacent banks of tubes; the walls of said heater including one end wall of each end unit, and the respective front and back walls of each of the units.

4. An air heater comprising in combination a plurality of assembled heat transference units connected side by side to form a unitary structure, said structure including two similar complemental end units and a generally similar unit therebetween; each of said units including a substantially rectangular bank of straight parallel tubes of relatively small diameter closely arranged in a staggered relationship but spaced from each other, a top tube plate and a bottom tube plate to which the ends respectively of said tubes are connected, and a casing for each bank of tubes surrounding said bank on the four sides thereof by four walls, said walls including a pair of end walls on opposite sides of each bank of tubes of a unit and a pair of walls constituting front and back walls, one of said last-mentioned pair of walls having an upper air inlet opening to the spaces between said tubes immediately below the top tube plate and extending for substantially the full width of said unit, and one of said pair of walls being provided with a. lower air outlet opening communicating with the spaces between the tubes immediately above the bottom tube plate and extending for substantially the full width of said unit, one of the end walls of each end unit completely closing the space between the upper and lower tube plates and extending between the front and back walls of each unit, the inner end walls of the end unit and both end walls of the intermediate unit being offset inwardly from the plane of the adjacent vertical side edges of the front and back walls of its unit and tightly closing for its full length the space between said front and back walls, the inner edges of the top and bottom tube plates of the end units being respectively joined to the complemental edges of the top and bottom tube plates of the intermediate unit; means to close the space between the upper ends of the offset end walls of adjacent units to form a chamber between said means and said top tube plate chamber from which incoming air is quickly and substantially uniformly distributed throughout the spaces between the tubes at the upper ends of adjacent banks of tubes; a hot gas box secured to the lower surface of said bottom tube plate for delivery of hot gases directly into the lower end of all of the tubes of said banks of tubes, and a similar box secured to the upper surface of the top tube plate into which the hot gases, after traveling through said tubes, are collected for discharge; the edges of the front and rear walls of the units being joined to the respective front and rear walls of adjoining units to provide the front and rear walls respectively of the heater, the outer end walls of the end units constituting the end walls of the heater.

5. An air heater comprising in combination a plurality of assembled heat transference sections connected together side by side to form a unitary structure, said structure including two similar complemental end sections and a generally similar section therebetween; each of said sections having a bank of straight parallel tubes of relatively small diameter closely arranged in a staggered relationship but spaced from each other, a top tube plate and a bottom tube plate to which the ends respectively of said tubes are connected, and a casing for each section surrounding the tubes of the section on four sides thereof by four walls, said walls including a pair of end walls on opposite sides of each section and a pair of walls constituting front and back walls of each section, one of said last-mentioned pair of walls of each section having an upper air inlet to the spaces between the tubes immediately below the top tube plate and extending substantially the full width of the section, and one of said pair of walls being provided with a lower air "outlet opening communicating with the spaces between the tubes immediately above the bottom tube plate and extending substantially the full width of the section, the outside end wall of each end section completely closing the spaces between the upper and lower tube plates and extending between the front and back walls of the section, the inner end wall of the end section and both end walls of the intermediate section being offset from the plane of adjacent vertical side edges of the front and back walls of its section and tightly closing for its full width the space between said front and back Walls of the section; the inner edges of the top and bottom tube plates and of the front and rear walls of the end section respectively being joined to the adjacent edges of the top and bottom tube plates and of the front and rear walls of the intermediate section; a plate closing the space between the upper ends of the offset end walls of adjacent sections; a hot gas box secured to the lower surface of said bottom tube plate for delivery of hot gases directly to the lower end of all the tubes of said banks of tubes, a similar box secured to the upper surface of the top tube plate into which the hot gases after travel through said tubes are collected for discharge, the edges of the front and rear walls of the units being joined to the respective front and rear walls of adjoining units to provide the front and rear walls respectively of the heater, the outer end walls of the end units constituting the end walls of the heater.

JOSIAH H. ROHRER. 

